Method of manufacturing a semiconductor device including a superlattice strain relief layer

ABSTRACT

A GaN/AlN superlattice is formed over a GaN/sapphire template structure, serving in part as a strain relief layer for growth of subsequent layers (e.g., deep UV light emitting diodes). The GaN/AlN superlattice mitigates the strain between a GaN/sapphire template and a multiple quantum well heterostructure active region, allowing the use of high Al mole fraction in the active region, and therefore emission in the deep UV wavelengths.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to provisional U.S. Applications forLetters Patent titled “Superlattice Strain Relief Layer ForSemiconductor Devices”, Ser. No. U.S. 60/736,362, and “Method ForControlling The Structure And Surface Qualities Of A Thin Film AndProduct Produced Thereby”, Ser. No. U.S. 60/736,531, each filed on Nov.14, 2005, each assigned to the same assignee as the present application,to which priority is hereby claimed, and each being incorporated byreference herein.

The present application is also related to and is a divisionalapplication of non-provisional U.S. Application for Letters Patenttitled “Superlattice Strain Relief Layer For Semiconductor Devices”,Ser. No. 11/356,769, filed Feb. 17, 2006, to which priority is herebyclaimed, and which is hereby incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with Government support under contract numberN66001-02-C-8017 awarded by the Defense Advanced Research ProjectsAgency, and contract number DAAH01-03-9-R003 sponsored by the U.S. ArmyAviation and Missile Command. The Government has certain rights in thisinvention.

BACKGROUND OF THE INVENTION

The present invention is related generally to the field of lightemitting diode devices, and more specifically to an architecture for animproved high-Al content, low defect heterostructure quantum wellsurface emitting light emitting diode device.

In the III-V compound semiconductor family, the nitrides have been usedto fabricate visible wavelength light emitting diode active regions.They also exhibit a sufficiently high bandgap to produce devices capableof emitting light in the ultraviolet, for example wavelengths between300 and 400 nanometers. In particular, InAlGaN systems have beendeveloped and implemented in visible and UV spectrum light emittingdiodes (LEDs), such as disclosed in U.S. Pat. No. 6,875,627 to Bour etal., which is incorporated herein by reference. These devices aretypically formed on an Al₂O₃ (sapphire) substrate, and comprisethereover a GaN:Si or AlGaN template layer, an AlGaN:Si/GaN superlatticestructure for reducing optical leakage, an n-type electrode contactlayer, a GaN n-type waveguide, an InGaN quantum well heterostructureactive region, and a GaN p-type waveguide region. In addition, thecomplete device may also have deposited thereover a p-type AlGaN:Mgcladding layer and a capping layer below a p-type electrode.

While significant improvements have been made in device reliability,optical power output, and mode stability, the performance of thenitride-based light emitting diode emitting in the ultraviolet (UV) isstill far inferior to that of blue or green light emitting diode. It isparticularly true that for the UV light emitting diodes, the nature ofthe substrate and template layer have a critical impact on the overalldevice performance. For example, electrical resistance between thestructural layers of the device significantly effects optical output.While Al₂O₃ (sapphire) as a substrate has numerous advantages, the AlGaNtemplate layer formed over the typical Al₂O₃ substrate posses highseries resistance due to limited doping capabilities. Furthermore, thecrystallographic structure of the device layers plays a key role in thedevice's operational characteristics, and the AlGaN template layerprovides a relatively poor crystalline template.

The dislocation densities in AlGaN or AlN template layers on sapphireare typically in the mid 10⁹ to high 10¹⁰ cm⁻² range. As a consequence,the external quantum efficiencies of deep UV light emitting diodes inthe 250 nm to 350 nm range are still below 2% even for the very bestdevices (external quantum efficiencies near 50% have been demonstratedfor blue GaN-based LED structures). The high dislocation densities inAlGaN or AlN template layers on sapphire also pose significant problemsfor the light emitting diode device lifetimes.

GaN epitaxial layers on sapphire substrates have proven to be a bettertemplate for InGaAlN film growth, providing excellent optoelectronicquality for visible light emitting diode devices and reasonabledislocation densities. The dislocation densities in GaN template layerson sapphire are typically in the low 10⁹ to mid 10⁷ cm⁻² ranges.Accordingly, sapphire with a GaN template layer is the preferredfoundation for visible GaN-based light emitting diodes.

The output wavelength of the light emitting diode is inversely relatedto the Al content in the multiple quantum well heterostructure (MQWH)active region of the device. Thus, in order to obtain shorter wavelengthdevices, such as those emitting in the UV, the Al content of the HQWHregion must be increased over that found in devices emitting in thevisible spectrum. However, increasing the Al content presents a numberof structural and device performance problems.

Furthermore, efforts to improve the quality of the LED structure in theultraviolet range on GaN/sapphire template have presented significantchallenges due to the large lattice mismatch between the epitaxiallayers formed over the GaN crystallographic template which is known tolead to strain-induced cracking. This lattice mismatch is exacerbatedwhen the Al content of layers formed above the GaN/sapphire systemincreases. Yet, as previously mentioned, an increased Al content (e.g.,up to ˜50% in the MQWH active region of a 280 nm light emitting diode,and 60% to 70% in the surrounding AlGaN current and optical confinementlayers) is required to obtain devices which emit in the UV. A UV InAlGaNheterostructure grown on GaN/sapphire is under tensile stress, whichcauses cracking of the AlGaN epitaxial layers when the critical layerthickness is exceeded. The critical thickness for an AlGaN film with a50% aluminum mole fraction is about 20-50 nm, which is much too thin forrealizing a usable device structure in the deep UV. Efforts to providestrain relief to accommodate the lattice mismatch have heretofore provenunsuccessful or impractical.

Various groups have published approaches to dealing with theseshortcomings. For example, Han et al., Appl. Phys. Lett, Vol 78, 67(2001), discuss the use of a single AlN interlayer formed at lowtemperatures to avoid strain development. This low-temperature AlNinterlayer approach has proven unsuccessful in the case ofheterostructure growth with high Al mole fractions. Nakamura et al., J.J. Appl. Phys., vol. 36, 1568 (1997) has suggested short periodGaN/AlGaN superlattice layers as a way of extending the critical layerthickness of AlGaN films grown pseudomorphically on GaN/sapphire. Butthe average Al mole fraction in these AlGaN/GaN systems is at such a lowlevel (˜10% or less) that it is not compatible with deep UV lightemitting diodes. Finally, Chen et al., Appl. Phys. Lett., vol. 81, 4961(2002) suggests an AlGaN/AlN layer as a dislocation filter for an AlGaNfilm on a AlGaN/sapphire template. But again, the AlGaN/sapphiretemplate presents the aforementioned series resistance problem. There isa need for a deep UV light emitting diode apparatus with improvedoperation characteristics, and therefore, there is a need for a methodand structure facilitating a high Al content MQWH active region which isfree from cracking and related damage.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a GaN/AlN strainrelief layer that enables the growth of crack-free thick AlGaN filmswith high aluminum content on a GaN/sapphire template. According to oneaspect of the present invention, an ultraviolet InAlGaN light emittingdiode heterostructure is grown on a GaN/sapphire template with a GaN/AlNshort period superlattice (SPSL) strain relief layer. The short periodsuperlattice strain relief layer enables the growth of a high-qualityand crack-free high aluminum content InAlGaN MQWH active region,providing a light emitting diode capable of emitting in the deep UVwavelength range. The GaN/AlN short period superlattice strain relieflayer may be formed in conditions (e.g., temperature and pressure)consistent with the growth of other layers of the device for efficientproduction.

Optionally, after growth, the deep UV light emitting diode may beflip-chip bonded onto a heatsink and the sapphire substrate removed byexcimer laser lift-off. The absorbing GaN template layer and some or allof the GaN/AlN short period superlattice strain relief layer may also beremoved, for example by dry-etching (e.g. by CAIBE). Removal of theGaN/sapphire template allows for improved light extraction through theUV-transparent AlGaN current spreading layer and results also in loweroperating voltages due to the vertical device structure.

According to another embodiment of the present invention, a GaN/AlNstrain relief layer enables the growth of low defect, relatively highAl-content films over a GaN/sapphire template useful for non-opticalapplications, such as the high electron mobility transistors (HEMTs) andthe like.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features, and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which like reference numerals denote likeelements between the various drawings, but which are not drawn to scale.

FIG. 1 is a cross-sectional view of a multiple quantum-wellheterostructure light emitting diode, including a GaN/AlN superlattice,according to an embodiment of the present invention.

FIGS. 2A-2F are illustrations of the steps involved in a laser lift-off(LLO) and etch process to produce a surface-emitting light emittingdiode according to an embodiment of the present invention.

FIG. 3 is a detailed view of a GaN/AlN superlattice structure accordingto an embodiment of the present invention.

FIG. 4 is a scanning electron microscope (SEM) view of a partialmultiple quantum-well heterostructure light emitting diode structuregrown on GaN/sapphire template, including a GaN/AlN superlattice,according to an embodiment of the present invention.

FIG. 5 is a voltage versus current graph, showing acceptable deviceperformance, for a deep UV light emitting diode grown on a GaN/sapphiretemplate with a GaN/AlN superlattice strain relief structure accordingto the present invention.

FIG. 6 is a graph of the Emission spectra (wavelength versus lightoutput), for a deep UV light emitting diode grown on a GaN/sapphiretemplate with a GaN/AlN superlattice strain relief structure accordingto the present invention.

FIGS. 7A-7D are SEM micrographs of a deep UV emitting diode grown on aGaN/sapphire template with the number of layers comprising thesuperlattice strain relief structure at zero, 20, 40, 60, and 80 layerpairs of GaN/AlN, respectively.

FIGS. 8A-8F illustrate an alternate embodiment of the production of asurface emitting LED according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference now to FIG. 1, there is shown therein an index guided,buried heterostructure AlGaInN light emitting diode structure 10 inaccordance with the present invention. Diode structure 10 comprises anAl₂O₃ (sapphire) substrate 12 on which is formed a 2-10 micron thickepitaxial GaN template layer 14. GaN template layer 14 can be Si-dopedor undoped and is typically grown at approximately 1100 degree C. and areactor pressure of approximately 200 Torr. Formed thereon is a GaN/AlNsuperlattice layer 16, described further below. Formed next is AlGaN:Sibuffer layer 18, and formed thereon is AlGaN/AlGaN:Si superlatticen-strain layer 20 which allows for increased cladding thickness andhence reduced optical leakage of subsequent layers. Formed next isAlGaN:Si n-cladding (index guiding) layer 22. InAlGaN multiple quantumwell active layer 24 is formed on layer 22. Formed thereon is AlGaN:Mgp-cladding (index guiding) layer 26, then AlGaN:Mg buffer layer 28.AlGaN/AlGaN:Mg p-strain layer 30 is next deposited, then finally aGaN:Mg capping layer is formed over the structure. The aforementionedlayers may be formed, for example, as described in the aforementionedincorporated U.S. Pat. No. 6,875,627 to Bour et al. It will beappreciated that a complete device will also include electrodes, notshown, as well as other similar or alternative devices formed in themanner of an array in appropriate embodiments.

The structure produced is a light emitting diode designed, for example,to emit UV light through the substrate. Since the GaN template layer isabsorptive at UV wavelengths, optimal device performance may be obtainedby removal of substrate 12 and GaN template layer 14. This maypreferably be accomplished by the method, referred to herein as a laserlift-off (LLO) process, described in U.S. Pat. No. 6,757,314, which isincorporated by reference herein. One embodiment of an LLO method bondsa combination substrate/heat sink to a surface opposite the Al₂O₃substrate. An excimer laser is typically employed to decouple the Al₂O₃substrate from the GaN layer, allowing removal of the substrate, the GaNlayer is then removed by a chemical process (e.g., dry etch). Some orall of GaN/AlN superlattice layer 16 is also removed by the chemicalprocess at this point. A variation on this method first bonds anintermediate wafer to a surface opposite the Al₂O₃ substrate. The Al₂O₃substrate and GaN layer are removed, and the device is then bonded toone of a variety of UV transparent substrates at the surface previouslyoccupied by the GaN layer and Al₂O₃ substrate. An example of such aprocess for removing the substrate and GaN template layer is illustratedin FIGS. 2A-2F, which merely schematically illustrate the light emittingdiode according to the present invention (i.e., not all layers thereofare shown in these figures.)

With reference first to FIG. 2A, a light emitting diode 34 (or an arrayof such devices) of a type described above is indirectly secured (e.g.,flip-chip, thermally, or acoustically bonded) to a substrate 36 withhigh thermal conductivity (such as copper, diamond, bulk AlN, orsilicon) to serve as a heat sink. Ideally, the first metal contact 38(p-contact) of the light emitting diode would be bonded to a solder40/AuTi 42 layer pair on substrate/heatsink 36 (which may or may not bepatterned), with the solder reflowing or deforming to form a permanentelectrical, thermal, and mechanical contact/bond between the lightemitting diode 34 and substrate/heat sink 36. In some cases thesubstrate/heatsink may be electrically conductive as well as thermallyconductive, providing an electrical contact to the first contact 38(p-contact) of the light emitting diode structure 34. In such cases anadditional contact layer 44 may be placed on the backside of thesubstrate/heatsink 36 to improve electrical contacting.

Reference is now made to FIG. 2B. With the light emitting diodestructure 34 affixed to substrate/heatsink 36, an excimer laser isscanned over the Al₂O₃ substrate 12. Due to the bandgap between GaN andits surrounding materials, there is high absorption of the light at theinterface between the Al₂O₃ substrate 12 and the GaN layer 14. Thiseffectively results in decomposition of the GaN material at thesapphire/GaN interface, weakening or breaking the bond between the twolayers. A second step to melt the transformed interface (typically attemperatures greater than the melting point of Ga (Tm ˜30 C°) willfurther weaken the interface bond. With the bond sufficiently weakened,the Al₂O₃ substrate 12 may simply be mechanically removed from the lightemitting diode structure 34, as shown in FIG. 2C.

The residual GaN layer 14 (typically several microns thick) and some orall of the GaN/AlN superlattice 16 are then removed using a dry etch(e.g., CAIBE) or possibly wet etching method. The structure is thensubstantially as shown in FIG. 2D. A second electrical contact 54(n-contact) is then patterned directly on the exposed InAlGaN lightemitting diode structure 52. This may be achieved in a variety of waysincluding (but not limited to) standard photolithography or a shadowmask processes. The structure is then as shown in FIG. 2E. The finallight emitting diode structure 56 permits light extraction through anupper surface, and electrical contact directly to the light emittingdiode active region via the contacts 44, 54 placed in direct contact onopposite sides of the active region.

With reference now to FIG. 3, there is shown therein an exemplaryembodiment of GaN/AlN superlattice 16, with layers grown in matchedpairs 56 with GaN grown on top of AlN (that is, AlN is grown first uponGaN layer 14, then a layer of GaN, then another layer of AlN, and soforth with GaN as the final layer in the superlattice 16, and upon whichAlGaN layer 18 is grown). Each of the superlattice pairs consists of anapproximately 7 Å wide GaN layer and an approximately 7 Å wide AlNlayer. The AlN and GaN layers are grown at approximately 1100 degree C°and approximately 200 Torr reactor pressure. The growth rate for the AlNand GaN layer was approximately ˜0.5 Å/sec. Superlattice layer 16 isnominally undoped, but could be doped (e.g., Si) by methods known in theart.

It will be appreciated that a critical role of GaN/AlN superlattice 16is to permit the incorporation of higher amounts of Al in subsequentlydeposited layers than previously possible, due to the reduced defects inlayers deposited over superlattice 16. However, forming each componentlayer of the superlattice 16 requires setting of processing equipmentcontrols and the introduction of constituent components, thus takingtime and consuming processing resources. Therefore, there is a balanceto be struck between growing a minimal number of layer pairs to simplifyprocessing and a sufficient number of pairs to allow for a crack-freehigh Al content heterostructure.

In quantifying this balance, the number of GaN/AlN superlattice pairswas varied between 20 and 80. Upon completion of a UV light emittingdiode structure of the type described with regard to FIG. 1, with an Almole fraction of the AlGaN layers at 25-40%, substrate 12, GaN templatelayer 14, and superlattice 16 were removed by processes described aboveand in aforementioned U.S. Pat. No. 6,757,314. The remaining completeddevices were examined for structural integrity, and surface condition ofAlGaN layer 18. (It is critical that AlGaN layer 18 be crack free so asto provide a suitable foundation for the subsequent layers, and furtherthat the multiple quantum well heterostructure active layer be crackfree for device performance.) Furthermore, optical performance of eachdevice was measured. A 20 pair superlattice 16 produced a device whichexhibited significant surface irregularity and cracks in the layer 18.Structural cracking decreased in structures with 40 superlattice pairs,but still showed some surface irregularity and cracks. Optimal results(freedom from structural cracks, surface smoothness, light emittingdiode performance, minimal number of layer pairs) were obtained for astructure which included a superlattice 16 consisting of 80 GaN/AlNpairs. At 80 superlattice pairs layer 18 showed virtually no detectabledamage or cracks. Table 1 summarizes these results. FIGS. 7A-7D are SEMmicrographs showing the visible results for this experiment.

TABLE 1 Number Of Light AlN/GaN Surface Light Emitting SuperlatticeAfter Led Emitting Diode Pairs Growth On Diode Relative SEM (All 7 Å /7Å) GaN/Sapphire Wavelength Intensity Photograph 0 Extremely Inoperableinoperable FIG. 7A heavily cracked 20 Heavily cracked 328.8 nm 1   FIG.7B 40 A few cracks 329.8 nm  1.45 FIG. 7C 80 Good, No cracks 328.3 nm3.6 FIG. 7D

Appropriate thicknesses of the superlattice layers were also explored byvarying each layer thickness between 7 and 14 Å for each of the GaN theAlN layers. The devices were prepared as previously described, and thesurface of layer 18 examined. The cracking seemed not to be affected bya change of superlattice layer thickness, although the x-ray diffractionexamination (XRD) at full-width half-maximum (FWHM) was the narrowestfor the case in which each of the GaN and AlN layers were each 7 Å inthickness. Table 2 summarize these results.

TABLE 2 AlN/GaN Superlattice (0006) XRD FWHM Thickness Of AlGaNEpitaxial (All 80 Pairs) Layer On GaN 7/7  Å 366″-785″ 7/14 Å 418″-680″14/7  Å 576″

FIG. 4 shows a cross-sectional SEM image of a UV light emitting diodeheterostructure 58, capable of emission at 325 nm. Layers notspecifically shown in FIG. 4 are either too thin to be seen in the SEMimage or have low contrast (because of layer doping) as compared withnearby layers. (E.g. The contact layer on top of the structure is only20 nm and can not be seen in the SEM picture). Structure 58 includes anAl2O3 substrate 60, a GaN:Si template layer 62 formed on and oversubstrate 60, an 80 layer-pair GaN/AlN superlattice 64 formed on andover GaN:Si layer 62, and an InAlGaN multiple quantum wellheterostructure layer 66 formed on and over superlattice 64. Each layerin superlattice 64 is approximately 7 Å thick. The Al content in layer66 was in the range of 35-40%. As can be seen, in cross section nocracks are visible in layer 66, a feature attributable to the provisionof superlattice 64 thereunder.

With reference to FIG. 5 device voltage versus current performance isshown for a deep UV light emitting diode grown on a GaN/sapphiretemplate with a GaN/AlN superlattice strain relief structure accordingto the present invention (performance measured after removal of thesubstrate, etching of the GaN and GaN/AlN superlattice and transfer ontoa quartz wafer) with peak emission around 327 nm. Likewise, withreference to FIG. 6, shown therein is the emission spectra of the UVlight emitting diode whose voltage-current data is shown in FIG. 5. Thecharacterization data shows that after LLO and transfer of the device toa quartz substrate, the Deep UV LED still has good device performance,i.e. good IV performance, and narrow and clean emission spectra whichindicate overall good material and device quality.

According to another embodiment for the production of a surface emittingLED shown in FIGS. 8A through 8F, a UV LED structure is transferred infabrication from a sapphire substrate to UV transparentmaterial/substrate via an intermediate host substrate. The intermediatehost substrate may be quartz, a flex substrate that facilitatesintegration of the LED device into larger systems, etc.

Initially, an intermediate (possibly UV transparent) substrate 70 isbonded to a surface of the UV LED structure opposite the sapphiresubstrate using an adhesive/epoxy, as shown in FIG. 8A. A LLO procedureis performed (as described previously), removing the sapphire substratefrom the GaN layer, as shown in FIGS. 8B and 8C. Etching then removesGaN layer 14 (optionally a sacrificial planarizaing layer 102 may beapplied prior to etching), leaving the LED active region 52 (as well asadditional layers) on the intermediate substrate, as shown in FIG. 8D.An n-contact layer 72 is then formed over the LED active region 52.Permanent substrate 74 is then bonded using a UV transparent epoxy(e.g., Epotek 301-2FL) to n-contact layer 72 (or alternatively, thesubstrate may form the n-contact, in which case substrate 74 is bondeddirectly to LED active region 52), as shown in FIG. 8E. In someinstances a protective layer(s) may be applied to the lateral sides ofthe LED to insure the UV transparent epoxy does not bond with theintermediate substrate.

Two optional embodiments are now possible, each illustrated in FIG. 8F.In the first, the LED structure is released from the intermediatesubstrate 58 by emersion in a solvent (e.g., acetone) that dissolves theepoxy bonding the intermediate substrate 58 to the structure.Intermediate substrate 58 is then removed, leaving a device in whichelectrical contact is made from the top while light is extracted fromthe bottom of the device. In the second, intermediate substrate is UVtransparent, and need not be removed. This also produces a device inwhich electrical contact is made from the top while the light isextracted from the bottom.

According to the present invention, a GaN/AlN strain relief layer formedover a GaN/sapphire template facilitates the formation of asubstantially defect-free relatively high Al-content layer thereover.While particularly useful in optical systems, the present invention mayalso find applicability in non-optical systems. For example, copendingU.S. patent application Ser. No. 10/952,202, which is incorporated byreference herein, discloses high electron mobility transistors (HEMTs)in which a relatively high Al-content AlGaN buffer layer is formed belowan undoped GaN layer. The provision of a GaN/AlN strain relief layer insuch a system may provide an improved quality AlGaN layer and henceimproved quality GaN layer, ultimately providing improved deviceperformance. Accordingly, another embodiment of the present inventionprovides a GaN/AlN strain relief layer for the growth of low defect,relatively high Al-content films over a GaN/sapphire template useful fornon-optical applications.

In a preferred embodiment of the present invention, a GaN/AlNsuperlattice is formed over a GaN/sapphire template to serve in part asa strain relief layer for growth of deep UV light emitting diodes.Furthermore, it has been demonstrated that a GaN/AlN superlattice can besuccessfully used to mitigate the strain between a GaN/sapphire templateand a high Al mole fraction deep UV light emitting diodeheterostructure. Deep UV light emitting diodes have successfully beengrown using this technique and working light emitting diodes have beendemonstrated, including devices having a substrate removed by excimerlaser lift-off. While this exemplary embodiment has been presented inthe foregoing detailed description, it should be understood that a vastnumber of variations exist, and this preferred exemplary embodiment ismerely a representative example, and is not intended to limit the scope,applicability or configuration of the invention in any way. Rather, theforegoing detailed description provides those of ordinary skill in theart with a convenient guide for implementation of the invention, and itis contemplated that various changes in the functions and arrangementsof the described embodiment may be made without departing from thespirit and scope of the invention defined by the claims thereto.

1. A method of manufacturing a semiconductor light emitting diodecomprising the steps of: forming over and in contact with a substrate aGaN template layer; forming over and in contact with said GaN templatelayer a superlattice structure, said superlattice structure comprising aplurality of layer pairs, a first layer of said layer pairs being AlNand a second layer of said layer pairs being GaN; forming over saidsuperlattice structure a multiple quantum well heterostructure of acomposition including at least 25% aluminum; forming a contact layerover said multiple quantum well heterostructure; securing a planar heatsink body to said contact layer; and thereafter removing said substrateand said GaN template layer; whereby said semiconductor light emittingdiode may emit light generally perpendicularly to the plane of the heatsink body.
 2. The method of manufacturing a semiconductor light emittingdiode of claim 1, further comprising the step of removing saidsuperlattice structure.
 3. A method of manufacturing a semiconductorlight emitting diode comprising the steps of: forming over and incontact with a substrate a GaN template layer; forming over and incontact with said GaN template layer a superlattice structure, saidsuperlattice structure comprising a plurality of layer pairs, a firstlayer of said layer pairs being AlN and a second layer of said layerpairs being GaN; forming over said superlattice structure a multiplequantum well heterostructure of a composition including at least 25%aluminum; forming a contact layer over said multiple quantum wellheterostructure; securing a transfer substrate to said contact layer;removing said substrate and said GaN template layer; securing saidsemiconductor light emitting diode to a planar heat sink body at asurface opposite said transfer substrate; and removing said transfersubstrate from said semiconductor light emitting diode; whereby saidsemiconductor light emitting diode may emit light generallyperpendicularly to the plane of the heat sink body.
 4. The method ofmanufacturing a semiconductor light emitting diode of claim 3, furthercomprising the step of removing said superlattice structure.